Evidence for Mesoarchean (?3.2 Ga) rifting of the Pilbara Craton: The missing link in an early Precambrian Wilson cycle

摘要

A sequence of c. 3.2 Ga low-grade sedimentary rocks, bimodal volcanic rocks, and subvolcanic layered mafic-ultramafic sills and dykes occur in greenstone belts that flank the margins of the 3.51-3.24 Ga East Pilbara Terrane of the Pilbara Craton, Western Australia. U-Pb SHRIMP zircon data and Sm-Nd model age data suggest that these rocks represent juvenile addition of material to the margins of the craton during a period of major extension, accompanied by the local emplacement of granitic rocks. This extensional event is also represented in adjacent terranes, by thick basalt flows with c. 3.2 Ga zircon and Sm-Nd model ages, and by granitic rocks. Based on the available age data, geochemistry of basaltic rocks, and the distribution of this event in space and time within the craton, we interpret the c. 3.2 Ga rocks to reflect widespread rifting of the protocraton and associated thinning of the lithosphere. This event resulted in separation of the flanking Kurrana and Karratha Terranes from their parent East Pilbara Terrane, which represents the ancient nucleus of the craton. These terranes were then reassembled during subsequent accretion at 3.07-2.905 Ga. Combined, the data suggest the preservation of a Mesoarchean Wilson cycle in the Pilbara Craton.